#include "serial.h"
#include "string.h"
#include "stdlib.h"

// COM1 - I/O ports
#define COM1_PORT_BASE 0x3F8

// RDR - Receive buffer register (on port read, if DLAB=0)
// THR - Transmitter holding register (on port write, if DLAB=0)
// DL - Divisor Latch (on port write, LSB, if DLAB=1) 
#define COM1_TRANSMIT_PORT COM1_PORT_BASE

// IER - Interrupt Enable Register (if DLAB=0)
// DL - Divisor Latch (on port write, MSB, if DLAB=1) 
#define COM1_INTERRUPT_ENABLE_PORT COM1_PORT_BASE + 1

// IIR - Interrupt Identification Register (on read)
// FCR - FIFO Control Register (write only)
#define COM1_FIFO_CONTROL_PORT COM1_PORT_BASE + 2

// LCR - Line Control Register
#define COM1_LCR_PORT COM1_PORT_BASE + 3

// MCR - Modem Control Register
#define COM1_MCR_PORT COM1_PORT_BASE + 4

// LSR - Line Status Register
#define COM1_LSR_PORT COM1_PORT_BASE + 5

// IER - Interrupt Enable Register
#define IER_ENABLE_IRQ_DATA_READY 0x01
#define IER_ENABLE_IRQ_WRITE_READY 0x02
#define IER_ENABLE_IRQ_STATUS 0x04
#define IER_ENABLE_IRQ_MODEM_STATUS 0x08 

// LSR - Line Status Register
#define LSR_THRE 0x20 // Transmitter Holding Register Empty 

// LCR - Line Control Register
#define LCR_DATA_BITS_5 0x00
#define LCR_DATA_BITS_6 0x01
#define LCR_DATA_BITS_7 0x02
#define LCR_DATA_BITS_8 0x03
#define LCR_ONE_STOPBIT 0x00
#define LCR_TWO_STOPBITS 0x04
#define LCR_PARITY_ENABLE 0x08
#define LCR_PARITY_EVEN 0x10
#define LCR_PARITY_STICKY 0x20
#define LCR_SET_BREAK 0x40
#define LCR_DLAB_ENABLE 0x80 // DLAB=1/0, baud rate DL register selector

// MCR - Modem Control Register
#define MCR_DTR_LOW 0x01
#define MCR_DTR_RTS_LOW 0x02
#define MCR_DTS_OUT2_LOW 0x04
#define MCR_LOCAL_LOOPBACK 0x08

// baud rate helpers (division of 115200 by divisor results in baud rate)
#define BAUD_RATE_DIVISOR_115200 1
#define BAUD_RATE_DIVISOR_57600 2
#define BAUD_RATE_DIVISOR_38400 3
#define BAUD_RATE_DIVISOR_19200 6
#define BAUD_RATE_DIVISOR_14400 8
#define BAUD_RATE_DIVISOR_9600 12
#define BAUD_RATE_DIVISOR_4800 24
#define BAUD_RATE_DIVISOR_2400 48
#define BAUD_RATE_DIVISOR_1200 96
#define BAUD_RATE_DIVISOR_300 384

void serial_init( serial_t *serial )
{
	memset( serial, 0, sizeof( serial_t ) );

	port8_init( &serial->port_transmit, COM1_TRANSMIT_PORT );
	port8_init( &serial->port_interrupt_enable, COM1_INTERRUPT_ENABLE_PORT );
	port8_init( &serial->port_fifo_control, COM1_FIFO_CONTROL_PORT );
	port8_init( &serial->port_line_control, COM1_LCR_PORT );
	port8_init( &serial->port_modem_control, COM1_MCR_PORT );
	port8_init( &serial->port_line_status, COM1_LSR_PORT );

	// disable all interrupts
	port8_write( &serial->port_interrupt_enable, 0x00 );

	// set baud rate, enable DLAB so we can access the DL registers
	port8_write( &serial->port_line_control, 
		LCR_DATA_BITS_8 | LCR_DLAB_ENABLE );
	port8_write( &serial->port_transmit, BAUD_RATE_DIVISOR_9600 );
	port8_write( &serial->port_interrupt_enable, 0 );
	port8_write( &serial->port_line_control, 
		LCR_DATA_BITS_8 );

	// disable FIFO (16550+ only, TODO: probe?)
	port8_write( &serial->port_fifo_control, 0x00 );

	// No loopback
	// TODO: more?
	port8_write( &serial->port_modem_control, 0x00 );
}

void serial_put_char( serial_t *serial, const char c )
{
	uint8_t status;
	do {
		status = port8_read( &serial->port_line_status );
	} while( ( status & LSR_THRE ) == 0 );
	
	port8_write( &serial->port_transmit, c );
}

void serial_put_string( serial_t *serial, const char *s )
{
	for( size_t i = 0; i < strlen( s ); i++ ) {
		serial_put_char( serial, s[i] );
	}
}

void serial_put_newline( serial_t *serial )
{
	serial_put_char( serial, '\r' );
	serial_put_char( serial, '\n' );
}